This invention relates to the field of general illumination in the crewmember work space of a night-operated vehicle; the desired illumination being compatible with night vision equipment.
The need to see objects and persons which are shrouded by darkness and the relatively advanced state of the solid state imaging systems art combine to make night vision equipment a desirable addition or retrofit in many types of military apparatus. Such capability is especially desirable, in the tactical military environment, where objects having a heat signature, such as energy dissipating vehicles and persons are to be detected in the dark. Frequently a capability of this type is needed as an addition to an existing piece of equipment, such as an older model aircraft. A need for such night vision capability also is found in the surveillance systems and security systems employed in civilian life.
Night vision equipment for these uses is usually operated on the principle of detecting the near or far infrared heat signature radiation from the objects being detected, or some fraction of the total near and far infrared spectrum. With presently available equipment, for example, it is possible for the pilot of an aircraft to readily detect moving vehicles while flying several thousand feet above the terrain of vehicle movement. The sensitivity of third generation night vision goggle apparatus may be appreciated from the fact that the infrared radiation from a lighted cigarette is sufficient to illuminate the objects in a large room for viewing with such goggle apparatus.
In the usual aircraft arrangement, therefore, night vision capability is afforded through the use of an electronic image binocular apparatus which includes an infrared responsive retina member and a solid state imaging display, all of which are located in a small package mounted on the pilot's helmet or otherwise arranged to be located between the pilot's eyes and the scene being viewed. Frequently the equipment of this type is arranged to be portable or of an add-on or retrofit nature for use with existing aircraft and for easy removal during other uses of the aircraft.
When infrared responsive apparatus of high sensitivity is operated in most aircraft cockpits, the operator soon realizes that an incompatibility exists between the infrared imaging apparatus and normal heat sources located within the aircraft cockpit. The lighting ordinarily used for instrument illumination, for control identification, and for normal human endeavors in the cockpit is particularly troublesome to night vision equipment. In addition to the basic receiving of energy from a nearby strong infrared source, in this scenario the tendency of sensitive infrared detectors to "bloom" or enlarge the physical size of a detected object in proportion to the intensity of the object's radiation causes a significant portion of the infrared detecting field to be disabled to a finite time period following the reception of images originating with such cockpit hotspots. A phenomenon of this type is frequently observed for example, when a television camera is focused on a sun reflecting object, a bright light, or a flame in a TV sportscast.
The present invention provides an improved aircraft cockpit lighting arrangement which of course may also be applied to land vehicles, water craft, surveillance equipment, and other uses where infrared responsive apparatus is threatened with the possibility of locally sourced large signal swamping. The present invention also offers a fast and convenient arrangement for changing the cockpit or vehicle control area lighting in order to accommodate infrared equipment--an arrangement which can easily be reversed to alternate or normal forms of cockpit lighting when needed.
The patent art includes several examples of lighting achieved with light emitting diode elements are disclosed in the present invention. This patent art includes the patent of Stephen W. Ray, U.S. Pat. No. 4,211,955, which concerns a solid state lamp having an integrated circuit chip fabricated light source. The Ray light source is enclosed in a bulb-like transparent envelope and mounted on a screw thread base so as to resemble a conventional incandescent lamp. The Ray apparatus additionally includes a rectifying circuit arrangement allowing excitation of the integrated circuit light emitting diode elements from either alternating current or direct current- and further includes an electronic circuit for regulating the current flow level in the light emitting diode elements. The provision of a directly interchangeable replacement unit for an incandescent filament lamp including the use of a similar package configuration, is an underlying concept of the Ray invention.
The patent art concerning illumination from a light emitting diode source also includes the commonly assigned patents of Yasuo Okuno, U.S. Pat. No. 4,298,869, and Jun-ichi Nishiazawa et al, U.S. Pat. No. 4,329,625, which concern the use of light emitting diode arrays in numeric displays, lamps, multi-color devices, and other lighted objects. Both the Okuno and Nishizawa et al patents include electrical circuit arrangements suitable for energizing light emitting diode devices, along with information concerning the electrical and optical characteristics of light emitting diode devices. The disclosure of these two patents is hereby incorporated by reference into the present specification.